Aerostatic lighter-than-air airships have seen substantial use since 1783, following the first successful manned flight of the Montgolfier brothers' hot-air balloon. Numerous improvements have been made since that time, but the design and concept of manned hot-air balloons remains substantially similar. Such designs may include a gondola for carrying a pilot and passengers, a heating device (e.g., a propane torch), and a large envelope or bag affixed to the gondola and configured to be filled with air. The pilot may then utilize the heating device to heat the air until the buoyant forces of the heated air exert sufficient force on the envelope to lift the balloon and an attached gondola. Navigation of such an airship has proven to be difficult, mainly due to wind currents and lack of propulsion units for directing the balloon.
To improve on the concept of lighter-than-air flight, some lighter-than-air airships have evolved to include propulsion units, navigational instruments, and flight controls. Such additions may enable a pilot of such an airship to direct the thrust of the propulsion units in such a direction as to cause the airship to proceed as desired. Airships utilizing propulsion units and navigational instruments typically do not use hot air as a lifting gas (although hot air may be used), with many pilots instead preferring lighter-than-air lifting gases such as hydrogen and helium. These airships may also include an envelope for retaining the lighter-than-air gas, a crew area, and a cargo area, among other things. The airships are typically streamlined in a blimp- or zeppelin-like shape, which, while providing reduced drag, may subject the airship to adverse aeronautic effects (e.g., weather cocking).
Airships other than traditional hot-air balloons may be divided into several classes of construction: rigid, semi-rigid, non-rigid, and hybrid type. Rigid airships typically possess rigid frames containing multiple, non-pressurized gas cells or balloons to provide lift. Such airships generally do not depend on internal pressure of the gas cells to maintain their shape. Semi-rigid airships generally utilize some pressure within a gas envelope to maintain their shape, but may also have frames along a lower portion of the envelope for purposes of distributing suspension loads into the envelope and for allowing lower envelope pressures, among other things. Non-rigid airships typically utilize a pressure level in excess of the surrounding air pressure in order to retain their shape and any load associated with cargo carrying devices is supported by the gas envelope and associated fabric. The commonly used blimp is an example of a non-rigid airship.
Hybrid airships may incorporate elements from other airship types, such as a frame for supporting loads and an envelope utilizing pressure associated with a lifting gas to maintain its shape. Hybrid airships also may combine characteristics of heavier-than-air airships (e.g., airplanes and helicopters) and lighter-than-air technology to generate additional lift and stability. It should be noted that many airships, when fully loaded with cargo and fuel, may be heavier than air and thus may use their propulsion system and shape to generate aerodynamic lift necessary to stay aloft. However, in the case of a hybrid airship, the weight of the airship and cargo may be substantially compensated for by lift generated by forces associated with a lifting gas such as, for example, helium. These forces may be exerted on the envelope, while supplementary lift may result from aerodynamic lift forces associated with the hull.
A lift force (i.e., buoyancy) associated with a lighter-than-air gas may depend on numerous factors, including ambient pressure and temperature, among other things. For example, at sea level, approximately one cubic meter of helium may balance approximately a mass of one kilogram. Therefore, an airship may include a correspondingly large envelope with which to maintain sufficient lifting gas to lift the mass of the airship. Airships configured for lifting heavy cargo may utilize an envelope sized as desired for the load to be lifted.
Hull design and streamlining of airships may provide additional lift once the airship is underway, however, previously designed streamlined airships, in particular, may experience adverse effects based on aerodynamic forces because of such hull designs. For example, one such force may be weather cocking, which may be caused by ambient winds acting on various surfaces of the airship. The term “weather cocking” is derived from the action of a weather vane, which pivots about a vertical axis and always aligns itself with wind direction. Weather cocking may be an undesirable effect that may cause airships to experience significant heading changes based on a velocity associated with the wind. Such an effect may thereby result in lower ground speeds and additional energy consumption for travel. Lighter-than-air airships may be particularly susceptible to weather cocking and, therefore, it may be desirable to design a lighter-than-air airship to minimize the effect of such forces.
On the other hand, airships having a hull shape with a length that is similar to the width may exhibit reduced stability, particularly at faster speeds. Accordingly, the aspect ratio of length to width (length:width) of an airship may be selected according to the intended use of the airship.
Landing and securing a lighter-than-air airship may also present unique problems based on susceptibility to adverse aerodynamic forces. Although many lighter-than-air airships may perform “vertical take off and landing” (VTOL) maneuvers, once such an airship reaches a point near the ground, a final landing phase may entail ready access to a ground crew (e.g., several people) and/or a docking apparatus for tying or otherwise securing the airship to the ground. Without access to such elements, the airship may be carried away by wind currents or other uncontrollable forces while a pilot of the airship attempts to exit and handle the final landing phase. Therefore, systems and methods enabling landing and securing of an airship by one or more pilots may be desirable.
In addition, airships may include passenger and/or cargo compartments, typically suspended below the hull of the airship. However, such placement of a passenger/cargo compartment can have an adverse affect on aerodynamics and, consequently, performance capabilities of the airship. For example, an externally-mounted compartment increases drag in both fore-aft and port-starboard directions, thus requiring more power to propel the airship, and rendering the airship more sensitive to cross-winds. Further, because an externally-mounted compartment is typically on the bottom of the airship, the compartment is offset from the vertical center of the airship and, therefore, may lead to instability as the added drag due to the compartment comes in the form of forces applied substantially tangential to the outer hull of the airship, causing moments that tend to twist and/or turn the airship undesirably. Such adverse moments require stabilizing measures to be taken, typically in the form of propulsion devices and/or stabilizing members (e.g., wings). However, propulsion devices require power, and stabilizing members, while providing stability in one direction, may cause stability in another direction. For example, a vertically-oriented stabilizer can provide lateral stability but may cause increased fore-aft drag, and may also render the airship more susceptible to cross winds. It would be advantageous to have an airship with a configuration that can carry passengers/cargo but is not susceptible to the adverse affects typically associated with externally-mounted compartments mentioned above.
The present disclosure is directed to addressing one or more of the desires discussed above, utilizing various exemplary embodiments of an airship.